When talking about limiting amino acids what does it really mean...
What I think it means is say we have a food eg wheat it has all the essential amino acids (aa) in it except one of them is not in the correct amount we need...does this mean that all the other aa present will not work or they will work but just limited to the limiting aa and the other amount will be degraded??--is this correct?

Also if essential aa needs are so low then would it be possible to say eat a burger (which said had 4/9 essential aa) and then say another food which had the other 5 essential aa would that be OK for the daily requirement?...so really we only have to eat a tiny bit in everyday life to get the aa??

An essential amino acid or indispensible amino acid, is an amino acid that cannot be synthesized de novo by the organism (usually referring to humans), and therefore must be supplied in the diet. Nutritional essentiality is characteristic of the species, not the nutrient. Nine amino acids are generally regarded as essential for humans. They are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. In addition, the amino acids arginine, cysteine, glycine and tyrosine are considered conditionally essential, meaning they are not normally required in the diet, but must be supplied exogenously to specific populations that do not synthesize it in adequate amounts. An example would be with the disease Phenylketonuria (PKU). Patients living with PKU must keep their intake of phenylalanine extremely low to prevent mental retardation and other metabolic complications. However, phenylalanine is the precursor for tyrosine synthesis. Without phenylalanine, tyrosine cannot be made and so tyrosine becomes essential in the diet of PKU patients.
Which amino acids are essential varies from species to species, as different metabolisms are able to synthesize different substances. For instance, taurine (which is not, by strict definition, an amino acid) is essential for cats, but not for dogs. Thus, dog food is not nutritionally sufficient for cats, and taurine is added to commercial cat food, but not to dog food.

The distinction between essential and non-essential amino acids is somewhat unclear, as some amino acids can be produced from others. The sulfur-containing amino acids, methionine and homocysteine, can be converted into each other but neither can be synthesized de novo in humans. Likewise, cysteine can be made from homocysteine but cannot be synthesized on its own. So, for convenience, sulfur-containing amino acids are sometimes considered a single pool of nutritionally-equivalent amino acids. Likewise arginine, ornithine, and citrulline, which are interconvertible by the urea cycle, are considered a single group.

LIMITING AMINO ACIDS

The limiting amino acids for lactating sows were determined using 28 primiparous sows that were intentionally underfed both energy and protein during a 21-d lactation. Groups of four sows were allotted to litter-size treatments of 6, 7, 8, 9, 10, 11, or 12 by cross-fostering as needed within 48 h postpartum. Sows were killed on d 21 of lactation. The carcass, liver, gastrointestinal tract, reproductive tract, mammary gland, and other viscera were separated, weighed, ground, and analyzed for dry matter, crude protein, and amino acids. Simple linear equations were obtained for each amino acid within tissues as a function of litter size. The mobilization of amino acids from carcass, liver, gastrointestinal tract, reproductive tract, and other viscera increased as litter size increased. Amino acids were accreted to mammary glands as litter size increased (2.65 g lysine/21 d for each one-pig increase in litter size). Milk production needs were estimated (49.9 g lysine/21 d for each one-pig increase in litter size). The quantity of each amino acid required additionally as litter size increased was obtained from the difference between amino acid needs for milk production and mammary gland growth and those provided from tissue mobilization. The relative ratio among amino acids that are required additionally (ideal amino acid pattern) was compared with the relative ratio of amino acids that can be provided from a corn-soybean meal lactation diet. From the comparison, it was shown that threonine and lysine are the first-limiting amino acids, followed by valine, when tissue mobilization occurs during lactation. Lysine is the first-limiting amino acid, and valine becomes second-limiting followed by threonine, when sows do not mobilize body tissues during lactation. Thus, the limiting order of essential amino acids changes depending on feed intake and tissue mobilization of sows during lactation. Proper feeding of lactating sows should consider the expected degree of tissue mobilization during lactation.